Aminopolycarboxylic acid chelating agents are well known and employed in combination with various metal ions in the chelated form for a variety of uses. One of the most effective ways of providing micronutrients to plants is to introduce the essential metal ion into the soil in the form of a chelate. Most of these are utilized in the fully chelated form, i.e. one mol of metal ion for each mol of chelant.
In British Pat. No. 1,094,781 there are disclosed compositions in which there is a combination of the metal salt together with the chelate of the same metal. Thus, a metal salt of zinc, e.g. zinc sulfate, was employed together with a zinc chelate, e.g. zinc nitrilotriacetate. An unexpectedly beneficial effect is alleged.
The problem with such salt-containing compositions is that the anions of some salts are phytotoxic, especially the sulfate, and others are undesirable to plants for one reason or another, sometimes depending upon in which part of the country they are to be used. When the zinc nitrilotriacetate is employed in solution, the solution can contain only minor amounts of the chelate since it has a low solubility in water. Thus, the application of zinc as a foliar-spray in this manner would not be practical.
It would, therefore, be desirable if a method could be found for preparing a solution of a zinc compound which would contain no undesirable anions.
It would also be desirable to find a solution of a zinc composition which could be employed as a foliar spray.
Such a solution and a method for preparing it has now been discovered and is the subject of the present invention.
A solution of partially chelated zinc ions has now been prepared by reacting an ammonium salt of ethylenediaminetetraacetic acid (EDTA) with an excess of an oxide or hydroxide of zinc and adding ammonium hydroxide to dissolve the excess unchelated zinc.
Solutions containing zinc/EDTA molar ratios of from 1.01 to 10 have been prepared and a total amount of zinc of up to 10% or more by weight in the solution.